Magnesium base alloy



Patented Nov. 7, 1939 2,178,576

2.178.575 MAGNESIUM BASE ALLOY John A. Gann, Midland, Mich., assignor to The Dow Chemical Company, Midland, Mich., a corporatlon of Michigan No Drawing. Original application January 13,

1937, Serial N0. 120,425. Divided and this application March 15, 1939, Serial No. 262,030

2 Claims. (Cl. 75-168) The present invention relates to magnesium alloys and particularly to those in which magnesium predominates.

Binary alloys of magnesium and copper have Similar property improvements were likewise obtained in the higher percentage copper alloys. For example/a binary magnesium-copper alloy containing 6 per cent of copper had the following been known for a long time, but they havenot properties: 5 been used commercially because of their relap area mechanical Properties and their Poor $1 32 l$52255?:3:53:3313358153:53:: 3:388 corrosion resistance. Elongation per cent 2 9 The primary object of this invention is to pro- 10 duce magnesium alloys containing copper, hav- The addition of 2 to 6 per cent of lead gave the 10 ing improved mechanical properties and corrowin i p v d p p s; sion resistance. Another object is to produce Tensile strength 20500 21200 magnesium alloys contaimng copper that are Yield strength in" 95G0 9,800 m nable to heat treatment. Qther obJects and Elongation "per cent 3.545 advantages will appear as the description proceeds The additional property improvements obtained The invention is based on the discovery that by adding f least One Of the low melting etals, the properties and characteristics of the binary till Z1110, t0 the above fiescllbed t y magnesium-copper alloys can .be enhanced very magneslulP'cfllpper-lead alloys are exempllfied y materially by the addition f definite amounts the fOHOWIIIgdIIUStI'atiODS. Aternary magnesium 20 of lead and that these ternary magnesium-copalloy contaimng 2 per ent of copper and 8 per per-lead alloys can be further improved by the n of lead had a 57 Strength of 5,900 pounds add t of definite amounts of t; least one of per square inch and a Brmell hardness of 37.0. th low-melting metals t and m The addition of 2 and 4 per cent of tin raised I have discovered that beneficial eirects due these values t A d poun s pe qu e 25 to the addition of lead to the binary magnesiuminch respect1ve1y n to 3 -1 and 42.2 Brmell copper alloys are obtained in general in alloys hardness sp t v y- An th r t rna y a containing from about 0.5 to 15 per cent of copnesillm alloy contaming 6 pe cent of copper d per to which has been added from about 0.5 to 20 6 per cent of lead had a yield strength of 9.800 per cent of lead. The amount of improvement Pounds D 111011 and a Brmell hardness 39 depends on the relative percentages of copper and 0f The addition of and 8 p t O 1 ad a d on the condition of the alloy, whether tin raised these values to 10,400, 12,600, and 13,000 cast, heat treated, or wrought. I have also dispounds p q a inch sp c iv ly. and t 4 covered that additional improvements in propand Brmell hardness respectively- I erties and in corrosion resistance can be obanother instance, a quat r y magnesium alloy 35 tained by adding certain percentages of tin and/ or iiQlltaimng 2 D t of pp T t OI l zinc to these ternary magnesium-copper-lead and 4 P cent of tin a W Strength of alloys. Such quaternary and quinary magnesium 7,200 pounds p q e i d a rmell hardalloys may contain from about 0.5 to 15 per cent 11858 f The additlon 0 and 8 per cent of copper, from about 0.5 to 20 per cent of lead, of zinc raised these properties to 8,700, 0,200, and 40 from about 0.5 to 10 per cent of tin, and from 11,300 pounds per square inch respectively, and about 0.5 to 10 per cent of zinc. For many purto 44.3, 45.6, and 48.9 Brinell hardness respecposes I prefer to use an alloy containing 80 per tively. Again, the ternary magnesium alloy concent or more of magnesium and 20 per cent or tainlng 2 per cent of copper and 2 per cent of 45 less of total added metals. lead had a tensile strength of 12,400 pounds per 45 The following examples serve to illustrate the square inch, a yield strength of 5,200 pounds per p p ty p v ts obtainable in these magsquare inch, and a Brinell hardness of 35.9. The n s umpp d a A as alloy addition of 8 per cent of zinc raised these proptaining 2 D cent of pp had the wi g erties to 22,600 pounds per square inch, 8,600 properties pounds per square inci, 231d a Blll'llgll hardness 50 of 44.3 respec ive y. im ar prope y improveig g ggg fi ments were likewise obtained in alloys contain- E1 cent 3 ing higher percentages of copper and/or lead.

onga 1 Many of the specific alloy compositions falling The addition of lead in amounts varying within the scope of this invention are amenable 55 3 to 3 Per cent gave alloys with the following to heat treatment. A solution heat treatment proved propert e r (S. H. T.) consisting of 16 hours at 425-450 0., Tensile strength lb./sq. in 13,500-16,700 for example, produced a marked increase in the Yield strength 1b./sq.in 5,300- 5,900 percentage elongation and impact toughness of 3.0-4.7 most of the alloys. Improvements amounting to c0 Elongation" --per cent-.

20-300 per cent were obtained, the amount of property improvement depending on the composition of the alloy. This treatment likewise resulted in a 10,, to 30 per cent improvement in the tensile strength of some of the alloys, particularly those containing appreciable amounts of zinc; and a subsequent precipitation heat treatment or aging (S. P. H. T.) for 16 hours at 175 C. resulted in still further property improvement, particularly in yield strength and hardness. This can be illustrated by the following examples:

Sand 8. P.

Property cast S. H. 'I H.

Tensile stren h ..1b lsq. in 21,200 28, 400 28, 200 Yield strengt 8, 500 8, 16, 100 longation 4. 2 8. 3 3. 0 Impac ft. 2. 9 8.9 4. 3 Brinell hardness 44. 3 44. 0 56. 5

Property S. H. T. Tensile strength lb.lsq. in 19, 900 26, 600 30,300 Yield strength .lb./sq. in.. ll, 300 10, 300 21, 600 Elongation pcroent l. 9 5. 5 l'. 6 Impact toughness it.-lb 1. 3 5. 6 2. 2 Brlnell hardness 48. 9 49. 4 66. 8

I have likewise discovered that the corrosion resistance of the magnesium-copper alloys may be markedly improved by the addition of lead and that the corrosion resistance of these ternary magnesium-copper-lead alloys may be still further improved by the addition of at least one of the metals, tin and zinc. In these investigations, the alloy specimens were subjected to an alternate immersion treatment in a 3 per cent solution of common salt (NaCl). The samples were in the salt solution approximately 15 seconds and then withdrawn and exposed to the air for approximately 2 minutes. This cycle was repeated continuously throughout the entire test. The loss weight was measured at the end of definite time intervals, usually 24 hours, and the results expressed as a decrease in the corrosion rate. The addition of lead, for example, in amounts varying from 2 to 8 per cent resulted in a 55 to 70 per cent reduction in the corrosion rate of the binary magnesium alloy containing 2 per cent of copper. In another instance the addition of 6 per cent of lead to a magnesium alloy containing 6 per cent of copper reduced the corrosion rate of the heat treated alloy by 68 per cent. It should be noted that heat treatment improved the corrosion resistance of the binary magnesiumcopper alloys, but that this effect appears to be carried over to the magnesium-copper-lead alloys where it is augmented by the beneficial effect due to the presence of lead.

It has likewise been discovered that the corrosion resistance of the new ternary magnesiumcopperlead alloys can be further improved by the addition of small amounts of at least one of the low melting metals, tin and zinc. For example, the addition of 2 per cent of tin to a magnesium alloy containing 2 per cent of copper and 8 per cent of lead reduced the corrosion rate by about 47 per cent, or about 83 per cent as compared to the original magnesium alloy containing 2 per cent of copper. The addition of 3 per cent of tin to a magnesium alloy containing 6 p r cent of copper and 6 per cent of lead was found to reduce the corrosion rate approximately 50 per cent, or about 84 per cent as compared to the original magnesium-copper alloy. Likewise, the addition of 8 per cent of zinc .to a magnesium alloy containing 2 per cent of copper, 8 per cent of lead, and 4 per cent of tin reduced the corrosion rate by 84 per cent, or 98 per cent as compared with the original magnesium alloy con taining 2 per cent of copper. Again, the addition of 8 per cent of zinc to a magnesium alloy containing 2 per cent of copper and 2 per cent of lead reduced the corrosion rate by about 98 per cent or about 99-per vcent as compared with the original magnesium alloy containing 2 per cent of copper. treatments have likewise been found beneficial in the case of these quaternary and quinary alloys.

The use for which the alloy is intended is an important factor in establishing its composition. Alloys with relatively high percentages of copper and relatively low percentages of lead, or of lead plus at least one of the metals tin and zinc, are best where high thermal properties are required. On the other hand, if corrosion resistance and properties obtainable by heat treatment are more important the alloys should, in general, contain a smaller percentage of copper than of lead, tin, and zinc. Alloys containing 2 to 10 per cent of copper and 2 to 10 per cent of lead; or 2 to 8 per cent of copper, 2 to 8 per cent of lead, and 2 to 8 per cent each of at least one of the metals tin and zinc are in general suitable for the production of castings. For extruded shapes, the alloy should preferably contain less than 12 per cent total added metal.

The above alloys may be prepared by the well known methods of melting magnesium with a protective flux and adding thereto the respective alloy ingredients, either singly or simultaneously. Cast products therefrom are made in dies or in sand containing an oxidation inhibitor, such as ammonium fluoride compounds. Heat treatment of the magnesium-copper alloys containing lead and lead plus tin may be conducted at 450 C. for approximately 15 to 30 hours, while the zincbearing alloys should be heat treated for the same time at approximately 425 C. 'Aging or precipitation heat treatment may be conducted for 18 to 24 hours at to C. Extruded Solution and precipitation heat shapes are produced by die extrusion at temperatures of 250 to 400 C.

This application is a division of my co-pending application Serial No. 120,426, filed January 13, 1937.

Other modes of applying the principle of my invention may be employed instead of those explained, change being made as regards the ingredients and,the steps herein disclosed, provided those stated by any of the following claims or their equivalent be employed.

I therefore particularly point out and distinctly claim as my invention:--

1. An alloy containing from about 0.5 per cent to 15 per cent of copper, from about 0.5 per cent to 20 per cent of lead, and from about 0.5 per cent to 10 per cent of zinc, the balance being magnesium.

2. An alloy containing from about 2 per cent to 8 per cent of copper, from about 2 per cent to 8 per cent of lead, and from about 2 per cent to 8 per cent of zinc, the balance being magnesium.

JOHN A. GANN. 

